This invention relates to a valve generally used to control a vacuum motor in response to a vacuum or pressure signal from a monitored source. More specifically, this invention relates to control of a vacuum operated idle-speed control system provided with a mechanism that responds rapidly to a very fast increase in vacuum from the monitored source. Delay valves are in wide spread use throughout the automotive industry to perform control functions. In the present case, a delay valve in a vacuum line may be connected to the idle control of an automobile engine through a controlling dashpot. The dashpot generally controls carburetor throttle opening in response to a signal from the delay valve which monitors a vacuum signal, such as the manifold vacuum of an internal combustion engine. The present delay valves have a time delay between a sensing of a vacuum level change in the manifold vacuum and the response or "delivery time" of that sensed change to the controlled element or device.
In an automobile, the failure of the dashpot to quickly respond to a rapid reduction in the manifold vacuum due to a delay valve leads to an open throttle, higher engine revolutions per minute (rpm's) and consequently added gas consumption. Present delay valve arrangements prevent the idle speed dashpot from compensating for suddenly changing engine conditions by providing relatively long time delays between an engine condition change and a response to that change in the dashpot, which change in the dashpot is based on the sensed engine change.
One method of controlling a segment of the above mentioned vacuum change is the avoidance of the use of a delay valve; however, this leads to erratic engine operating conditions and added pollution control problems. Alternatively, a control arrangement of bypassing a delay valve, under a given condition or after a fixed parameter is exceeded, is preferred. Such a bypass arrangement allows a delay valve to operate in the present mode under most conditions while overcoming the circumstance where there is a rapid change in the monitored condition, such as a deceleration which causes a rapid decrease in engine manifold vacuum from atmospheric pressure. These sudden changes in vacuum levels are frequently experienced by an automotive engine, especially in such conditions as rapid acceleration and rapid deceleration.